The frequency of aircraft freighter main deck cargo fires has increased over the years. Recent NTSB Safety Recommendations to the FAA (Nov. 28, 2012 A-12-68 through 70) suggest various guidelines, including: developing and implementing fire detection system performance requirements for the early detection of fires originating within cargo containers and pallets (A-12-68). (This safety recommendation supersedes Safety Recommendation A-07-98, which is classified “Closed-Acceptable Action/Superseded.”); ensuring that cargo container construction materials meet the same flammability requirements as all other cargo compartment materials in accordance with Title 14 Code of Federal Regulations 25.855. (A-12-69); and requiring the installation and use of active fire suppression systems in all aircraft cargo compartments or containers, or both, such that fires are not allowed to develop (A-12-70).
Conversion of passenger aircraft to freighter aircraft is a common practice. Passenger aircraft typically includes a cargo hold or deck for transporting passenger baggage and other cargo and a main deck for transporting passengers. The cargo deck of a passenger aircraft typically includes smoke detection and fire suppression, for example using smoke and/or heat detectors for fire detection and an extinguishing gas or retardant source such as one or more Halon or other fire retardant canisters for dispersion of suppressant. Passenger deck fire suppression typically includes hand-held fire extinguishers delivered by an operator. System level fire protection with the use of an extinguishing gas source in a passenger cabin is not standard practice as this environment is an occupied space and use of portable fire extinguisher is common practice.
Conversion of passenger aircraft to freighter aircraft is a common practice. Passenger aircraft typically include a cargo hold for transporting passenger baggage other cargo and a main deck for transporting passengers. The cargo hold of a passenger aircraft typically includes a system for detecting fires, for example using smoke and/or heat detectors inside the cargo hold, and a system for controlling fires through use of fire resistant materials, reducing airflow, and flooding the entire cargo hold with active fire suppressing or inert gases that are remotely discharged from the flight deck. The passenger compartment on the main deck typically relies on the flight crew for fire detection, with the exception of certain spaces such as lavatories and, in some cases, galleys. Fire suppression in the passenger compartment typically uses hand held portable extinguishers operated by the flight crew. A total flooding approach to fire suppression in a passenger compartment is not typically standard practice as this space is occupied by humans.
Conversion of a passenger aircraft to an aircraft that can carry freight in place of passengers on the main deck typically includes the addition of a fire or smoke detection system, fire resistant main deck cargo liners, and a way to deprive the fire of oxygen to control the fire. Fire protection within existing cargo holds is not typically modified during conversion of the aircraft from a passenger plane to a freighter. Freighter aircraft have typically used decompression of the main deck cargo space as the technique to deprive the fire of oxygen, this approach is commonly referred to as passive fire suppression. For decompression to be an effective technique for controlling a main deck fire, the aircraft must be flying at an altitude high enough that the oxygen is forced out of the aircraft and the ambient oxygen available is insufficient to allow the fire to grow. Typically, the minimum altitude used for effectively controlling a main deck fire is 25,000 feet above sea level. The overall effectiveness of this approach has been questioned (reference the NTSB Safety Recommendations discussed above), as the aircraft must eventually descend to land, which increases oxygen levels and can cause the smoldering fire to reignite and expand out of control. The NTSB has thus recommended the addition of an active fire suppression system to the main deck fire protection scheme of freighter aircraft.
To apply the same total flooding active fire suppression techniques on the main deck that are used for the standard cargo holds of passenger aircraft is problematic due to the large volume of the main deck cargo compartment relative to the cargo holds of the lower deck. The weight of a fire detection and suppression system increases with the volume of area to be protected, for example because the volume of gas is increased. Aviation products/systems are particularly sensitive to increased weight, for example because the cost of hourly operation from fuel and other costs increases as payload weight increases.
For example, an initial discharge system (i.e., high rate discharge, HRD) for a lower deck cargo hold of a 747-400 may require about 110 pounds of Halon to achieve a 6.8% maximum concentration forward and 6.2% aft. This quantity of Halon provides a 5% Halon concentration in about 2 minutes and a maximum concentration in about 3 minutes. A metered discharge system (i.e., low rate discharge, LRD) for a cargo deck may require about 160 pounds of Halon to achieve a sustained concentration of about 3.7% forward for a sustained duration of about 3% for a duration of greater than 195 minutes. An HRD system for a main deck of a 747-400 may require about 294 pounds of Halon to achieve a 7.0% maximum concentration. This quantity of Halon provides a 5% Halon concentration in about 40 seconds and a maximum concentration in about 1 minute. An LRD system for the main deck may require about 920 pounds of Halon to achieve a sustained concentration of about 3.2% for a duration of greater than 90 minutes. Halon gross weight for the 747-400 is about 410 pounds for the lower deck cargo holds and about 1680 pounds for the main deck.
A fire suppression system and method is disclosed in US Pat. Pub. 2010/0236796, which is incorporated herein by reference in its entirety.
A fire suppression and containment system that assists in meeting these recommendations, improves detection time for smoke/ fires, reduces fire damage, and decreases weight compared to some other fire protection systems would be desirable.